The highway widening is very important component of highway construction in china. To the subgrade widening, the steps excavation of the old side slope and the new embankment construction in layers is the methods to be used commonly at the new and old subgrade interaction part in the subgrade widen project. Combined the reality of many highway widening projects about the steps excavation at he new and old subgrade interaction part, defined four plans of the steps excavation. According to the actual Hatong highway widening project, the geometric analyzing model was determined, and the physical and mechanical parameters of soil were got by the test of the site survey and different soil. The numerical simulation and the analysis was done by using the elastic-plasticity finite element software ABAQUS to the different steps excavation and new embankment construction. The appropriate step excavation plan was suggested and the main corresponding construction points were given. The results have the practical significance to enhance the effective union of the new and the old subgrade, reduces the unequal settlement of the new and old subgrade and reduces to the old road’s damage.